Sheet-shaped objects such as integrated circuits and liquid crystal display panels are generally inspected using a probe device exemplified by a probe card and a probe unit.
JP 2001-141747 A describes a probe device used to conduct an energization test of display circuit boards used in display devices such as liquid crystal display panels.
The probe device 10 described in JP 2001-141747 A connects a plurality of sheets each having a plurality of lines formed by photolithography on one surface of an electrically insulating film 38. The lines extend parallel to each other in forward and backward direction, spaced apart in left and right direction, as illustrated in FIG. 7. A first connection sheet 20 has a plurality of lines 34 and 36 formed by a circuit printing technique on one surface of the electrically insulating film 38 such as one made of polyimide and has a TAB-mounted chip (integrated circuit) 40 electrically connected to the lines 34 and 36 on the one surface. The TAB-mounted chip (integrated circuit) 40 is connected to a probe sheet 18, and the first connection sheet 20 is electrically connected to a second connection sheet 22.
In an energization test (in an inspection process), test signals are supplied to the TAB-mounted chip (integrated circuit) 40 via a wiring member 46, the second connection sheet 22, and the first connection sheet 20, with projecting electrodes 30 provided at the foremost end portions of the lines on the probe sheet 18 pressed against respective electrodes 44 of the display circuit boards of a liquid crystal panel 42 as illustrated in FIG. 6.
The probe sheet 18, attached to the underside of a probe holder 24, constitutes a probe block. The probe holder 24 can be attached to or detached from the underside of the forward end portion of a probe base 48 by moving the probe holder 24 forward and backward relative to the probe base 48 and is removably secured to the probe base 48 by means of a screw member 49.
As illustrated in FIG. 6, the lines on the probe sheet 18 are electrically connected to the lines on the wiring member 46 provided on the underside of the probe base 48 via the lines on the first connection sheet 20 and the lines on the second connection sheet 22 provided on the underside of the probe holder 24.
Thus, in the display circuit boards of the liquid crystal panel 42, drive signals are supplied via the TAB-mounted chip (integrated circuit) 40, the first connection sheet 20, and the probe sheet 18 to the electrodes 44 determined by an input signal.
However, the TAB-mounted chip (integrated circuit) 40 is used as the first connection sheet 20 and, in addition, the foremost end portion of the TAB-mounted chip is bonded to the probe sheet 18 although the probe, in particular the probe sheet 18, of the above conventional device needs to be replaced occasionally because of worn or broken projecting electrodes 30.
Therefore, to replace the probe sheet 18, the probe sheet 18 needed to be peeled off from the first connection sheet 20, and in the process, lines on the first connection sheet 20 were often broken, necessitating replacement of also the first connection sheet 20.
Therefore, a study is being made of a possibility of using, in place of the TAB-mounted chip, an anisotropic conductive film (of conductive particles-containing resin type) 54 wherein, as illustrated in FIG. 4, the respective electrodes of a circuit board 58, corresponding to the first connection sheet, and a circuit board 70, corresponding to the probe sheet, are electrically connected by dispersing fine conductive particles 52 in a resin 50, and wherein the circuit boards 58 and 70 are bonded to each other under pressure to establish electrical connection. However, because the electrical connection through the anisotropic conductive film 54 is achieved by using the property thereof, i.e., by allowing the thermoplastic resin 50 to penetrate the non-electrode portion, the anisotropic conductive film 54 was often broken when the resin 50 and the circuit board 70, serving as the probe sheet, bonded to each other at a portion 56 where the resin and the circuit board are in contact, are detached from each other for replacement. An attempt to solve the above problem by not bonding the probe sheet and the resin of the anisotropic conductive film results in, for example, electrical disconnection between the lines on the probe sheet 18 and the lines on the first connection sheet 20 illustrated in FIG. 7 in the mounting process.
JP 2008-270158 A proposes an anisotropic conductive material wherein conductive members penetrate a film made of an insulating material.
JP 2009-224146 A describes studying a possibility of a technique of connecting a circuit board 58 and an electronic component 68 using an anisotropic conductive film 60 having transmembrane electrodes in an inorganic insulating film as illustrated in FIG. 5.
However, the inventors of the present invention found the following problems in using an anisotropic conductive film that employs an inorganic film.
There is practically a variation 62 in height among the electrodes within a circuit board. For the inorganic film alone to compensate for the height variation, the film, a hard, inorganic film, needs to warp. The warping causes a distortion 66 in the anisotropic conductive film 60, which may cause the film to break. In addition, ever smaller pitches are reducing the distance between electrodes, so that there is a limit to the extent to which the warping of the anisotropic conductive film can compensate for the distortion 66 caused in the anisotropic conductive film.
The present inventors made an in-depth study on resin-made anisotropic conductive films and inorganic anisotropic conductive films to solve the above problems.
The contact of the circuit board 70 and the anisotropic conductive film 54 is mostly making detachment of the circuit board 70 from the anisotropic conductive film 54 shown in FIG. 4 difficult. When, in particular, use is made of a resin-made anisotropic conductive film, the affinity with the resin layer forming the surface of the circuit board is so great as to result in bonding when the close contact is allowed to last for a long time. To avoid this, the thickness of the anisotropic conductive film needs to be smaller than that of the electrodes so that the anisotropic conductive film resin does not invade the non-electrode portion. In order to reduce the thickness of the anisotropic conductive film and still secure connection reliability, increasing the density of the conductive particles is essential, but further increasing the present density is difficult.
Hardening the resin may be one of the means but would reduce the probability of connection achieved by the conductive particles and reduce the connection reliability.
On the other hand, an anisotropic conductive material using an inorganic anisotropic conductive film, whose matrix is composed of a hard film, only contacts metallic electrodes because of its properties, and contact with a circuit board is avoided, which makes an anisotropic conductive material effective in avoiding the above problems. However, such anisotropic conductive material still cannot address the problem of the electrode height variation. Addressing the electrode height variation requires the use of a component capable of plastic deformation. There are two kinds of height variation: one occurring within one electrode surface, i.e., one caused by a surface roughness of the plated surface; the other attributable to a variation in plating among electrodes. The variation of the former kind is about 1 μm; the variation of the latter kind is about 2 μm to 5 μm. It is possible that the variation of the former kind is related to the elasticity of the film with respect to the electrode dimensions; the variation of the latter kind is related to the elasticity of the film with respect to the distance between the electrodes.
In the case of the variation of the latter kind, specifically a small inter-electrode distance resulting from ever decreasing inter-electrode pitches in the industry increases the ratio (R/L) of plating-caused variation length (R) to the inter-electrode distance (L), making it difficult to address the problem with an inorganic film.